Transmission apparatus, reception apparatus and digital radio communication method

ABSTRACT

A transmission method includes modulating a transmission signal using a modulation scheme selected from a plurality of modulation schemes, to generate a first symbol sequence and generating at least one second symbol including a pilot symbol generated using a PSK modulation scheme. The method includes changing an insertion interval of the second symbol to be inserted in the first symbol sequence, to generate a modulation signal and transmitting the modulation signal. The second symbol is configured for synchronization in a reception apparatus.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 13/613,407, filed on Sep. 13, 2012, which is a continuation ofU.S. patent application Ser. No. 12/206,427, filed on Sep. 8, 2008, nowU.S. Pat. No. 8,295,399, which is a continuation of U.S. patentapplication Ser. No. 11/955,443, filed Dec. 13, 2007, now U.S. Pat. No.7,545,882, which is a divisional application of U.S. patent applicationSer. No. 10/827,445, filed Apr. 20, 2004, now U.S. Pat. No. 7,359,457,which is a continuation of U.S. patent application Ser. No. 09/627,070,filed Jul. 27, 2000, now U.S. Pat. No. 6,993,092, the disclosures ofwhich are expressly incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a transmission apparatus, receptionapparatus and digital radio communication method, which is used fordigital radio communications.

Description of the Related Art

As a conventional digital modulation system, a technology described inthe Unexamined Japanese Patent Publication No. HEI 1-196924 is known.This is the technology which the transmitting side configures a frame byinserting 1 known pilot symbol for every N data symbols and thereceiving side estimates a frequency offset and amount of amplitudedistortion by using the pilot symbol, and removes these frequency offsetand amplitude distortion and demodulates.

Here, in the case of a radio communication, fluctuations in thetransmission path occur due to fading and in terrestrial mobilecommunication in particular, fluctuations in the transmission path arenot uniform. When fluctuations in the transmission path are intense, theinterval of inserting a pilot symbol must be shorter to preventdeterioration of the data demodulation error rate. On the contrary, whenfluctuations in the transmission path are gentle, extending the intervalof inserting a pilot symbol does not deteriorate the data demodulationerror rate so much.

On the other hand, when the level of a reception signal on the receivingside is small, a modulation system used must be highly resistant toerrors for information symbols. On the contrary, when the level of areception signal on the receiving side is large, higher priority can begiven to a modulation system of high transmission efficiency forinformation symbols.

However, in the conventional digital modulation system above, the pilotsymbol insertion interval and the information symbol modulation systemare fixed. Therefore, when fluctuations in the transmission path areintense or the level of the reception signal of the receiver is small,error resistance during data demodulation reduces and the quality ofdata deteriorates. On the other hand, when fluctuations in thetransmission path are gentle or the level of the reception signal on thereceiving side is large, the data transmission efficiency cannot beimproved despite the excessive data quality.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a transmissionapparatus, reception apparatus and digital radio communication methodcapable of flexibly improving the data transmission efficiency and thequality of data.

The present invention attains the above object by changing the intervalof inserting a known pilot symbol, binary phase (BPSK: Binary PhaseShift Keying) modulation symbols or quadrature phase (QPSK: QuadraturePhase Shift Keying) modulation symbols and the modulation system ofinformation symbols according to the communication situation such asfluctuations in the transmission path and the level of a receptionsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawing wherein one example isillustrated by way of example, in which;

FIG. 1 is a block diagram showing a configuration of a transmissionapparatus according to Embodiment 1 of the present invention;

FIG. 2 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of Embodiment 1 of thepresent invention;

FIG. 3 is a layout of signal points of 16QAM and a known pilot symbol onan in-phase I-quadrature Q plane;

FIG. 4 is a layout of signal points of 8PSK modulation and a known pilotsymbol on an in-phase I-quadrature Q plane;

FIG. 5 is a block diagram showing a configuration of a receptionapparatus according to Embodiment 1 of the present invention;

FIG. 6 is a block diagram showing a configuration of a transmissionapparatus according to Embodiment 2 of the present invention;

FIG. 7 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of Embodiment 2 of thepresent invention;

FIG. 8 is a layout of signal points of 16QAM and BPSK modulation on anin-phase I-quadrature Q plane;

FIG. 9 is a layout of signal points of 8PSK modulation and BPSKmodulation on an in-phase I-quadrature Q plane;

FIG. 10 is a block diagram showing a configuration of a receptionapparatus according to Embodiment 2 of the present, invention;

FIG. 11 is a block diagram showing a configuration of a transmissionapparatus according to Embodiment 3 of the present invention;

FIG. 12 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of Embodiment 3 of thepresent invention;

FIG. 13 is a layout of signal points of 16QAM and QPSK modulation on anin-phase I-quadrature Q plane;

FIG. 14 is a layout of signal points of BPSK modulation and QPSKmodulation on an in-phase I-quadrature Q plane;

FIG. 15 is a block diagram showing a configuration of a receptionapparatus according to Embodiment 3 of the present invention;

FIG. 16 is a block diagram showing a configuration of a transmissionapparatus according to Embodiment 4 of the present invention;

FIG. 17 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of Embodiment 4 of thepresent invention;

FIG. 18 is a layout of signal points of BPSK modulation on an in-phaseI-quadrature Q plane;

FIG. 19 is a layout of signal points of QPSK modulation on an in-phaseI-quadrature Q plane;

FIG. 20 is a block diagram showing a configuration of a receptionapparatus according to Embodiment 4 of the present invention;

FIG. 21 is a block diagram showing a configuration of a transmissionapparatus according to Embodiment 5 of the present invention;

FIG. 22 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of the Embodiment 5 of thepresent invention;

FIG. 23 is a layout of signal points of 16QAM, a known pilot symbol andsymbols before and after the pilot symbol on an in-phase I-quadrature Qplane;

FIG. 24 is a layout of signal points of 8PSK modulation, a known pilotsymbol and symbols before and after the pilot symbol on an in-phaseI-quadrature Q plane; and

FIG. 25 is a block diagram showing a configuration of a receptionapparatus according to Embodiment 5 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below.

Embodiment 1

Embodiment 1 describes a digital radio communication method by which theinterval of inserting a known pilot symbol and the modulation system ofinformation symbols are changed according to the communicationsituation.

FIG. 1 is a block diagram showing a configuration of a transmissionapparatus according to this embodiment. As shown in FIG. 1, thetransmission apparatus according to this embodiment mainly consists offrame configuration determination section 101, quadrature basebandmodulation section 102, pilot symbol generation section 103, frameconfiguration section 104, and LPFs (Low Pass Filters)105 and 106,transmission radio section 107 and transmission antenna 108.

Frame configuration determination section 101 judges the communicationsituation based on transmission path information which shows the degreeof fluctuations of the transmission path due to fading and datatransmission speed information which shows the transmission speed oftransmission data based on the level of a reception signal and decidesthe interval of inserting a known pilot symbol and the modulation systemof a transmission digital signal. Then, frame configurationdetermination section 101 outputs a signal indicating the determinedmodulation system to quadrature baseband modulation section 102 andoutputs a signal indicating the determined interval of inserting theknown pilot symbol to frame configuration section 104. By the way,details of the method of determining a frame configuration by frameconfiguration determination section 101 will be described later.

Here, when an identical frequency band is used for the uplink and thedownlink, the situation of fluctuations in the transmission path due tofading can be estimated from a transition in the result of measuring thereception level of the modulated signal transmitted from the other endof communication on the receiving side, which is not shown in thefigure, of the communication apparatus in which the transmissionapparatus shown in FIG. 1 is mounted. Furthermore, the transmissionapparatus shown in FIG. 1 can recognize the situation of fluctuations inthe transmission path due to fading, by the reception apparatus, whichis the other end of communication of the transmission apparatus shown inFIG. 1, measuring the reception level of the modulated signaltransmitted from the other end of communication, estimating thesituation of fluctuations in the transmission path due to fading basedon the transition of the measurement result.

Then, when an identical frequency band is used for the uplink and thedownlink, the transmission speed of the transmission data can bedetermined from a result of measuring the reception level of themodulated signal transmitted from the other end of communication on thereceiving side, which is not shown in the figure, of the communicationapparatus in which the transmission apparatus shown in FIG. 1 ismounted. Furthermore, the transmission apparatus shown in FIG. 1 canrecognize the transmission speed of the transmission data by thereception apparatus, which is the other end of communication of thetransmission apparatus shown in FIG. 1, measuring the reception level ofthe pilot symbol transmitted from the other end of communication anddetermining the transmission speed of the transmission data based on themeasurement result.

Quadrature baseband modulation section 102 modulates a transmissiondigital signal to a quadrature baseband signal with the modulationsystem indicated from frame configuration determination section 101 andoutputs the in-phase component and the quadrature component of thequadrature baseband signal to frame configuration section 104.

Pilot symbol generation section 103 generates a pilot symbol knownbetween the transmitting and receiving sides and outputs the in-phasecomponent and the quadrature component of the known pilot symbol toframe configuration section 104.

Frame configuration section 104 inserts the known pilot symbol outputfrom pilot symbol generation section 103 into the output signal ofquadrature baseband modulation section 102 at the insertion intervalinstructed from frame configuration determination section 101 andcomposes a frame.

LPF 105 lets pass only a predetermined frequency band section of thein-phase component output from frame configuration section 104, LPF 106lets pass only a predetermined frequency band section of the quadraturecomponent output from frame configuration section 104.

Transmission radio section 107 transmits a radio frequency signal as theelectric wave from transmission antenna 108 after performing radioprocessing on the output signals of LPF 105 and LPF 106.

Next, examples of the method of determining a frame configuration byframe configuration determination section 101 of the transmissionapparatus shown in FIG. 1 above will be explained.

FIG. 2 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of this embodiment and showsa time-symbol relationship. (201) is a frame configuration when themodulation system of information symbols is 16-value quadratureamplitude modulation (16QAM: 16 Quadrature Amplitude Modulation) and aknown pilot symbol interval is N symbols. (202) is a frame configurationwhen the modulation system of information symbols is 16QAM and a knownpilot symbol interval is M symbols. (203) is a frame configuration whenthe modulation system of information symbols is 8 phases (8PSK: 8 PhaseShift Keying) modulation and a known pilot symbol interval is N symbols.(204) is a frame configuration when the modulation system of informationsymbols is 8PSK modulation and a known pilot symbol interval is Msymbols. Suppose N<M at this time.

Frame configuration determination section 101 selects one of (201),(202), (203) or (204) in FIG. 2 as the optimal frame configuration basedon the transmission path information and the request data transmissionspeed information.

For example, in the case of high-speed fading, frame configurationdetermination section 101 sacrifices data transmission efficiency on thereceiving side and selects a frame configuration of either (201) or(203) in FIG. 2 so that the interval of inserting a known pilot symbolbecomes narrower to prevent deterioration of the data demodulation errorrate and maintain the quality of data. On the other hand, in the case oflow-speed fading, frame configuration determination section 101 selectsa frame configuration of either (202) or (204) in FIG. 2 to widen theinterval of inserting a known pilot symbol to improve the datatransmission efficiency.

Also, when the level of the reception signal is large, frameconfiguration determination section 101 gives priority to datatransmission efficiency on the receiving side and selects a frameconfiguration of either (201) or (202) in FIG. 2 adopting 16QAM as themodulation system of information symbols. On the other hand, when thelevel of the reception signal is small, frame configurationdetermination section 101 gives priority to increasing error resistancewhile sacrificing data transmission efficiency on the receiving side andselects a frame configuration of either (203) or (204) in FIG. 2adopting 8PSK as the modulation system of information symbols.

FIG. 3 shows a signal point layout according to the 16QAM modulationsystem on the in-phase I-quadrature Q plane and signal point layout of aknown pilot symbol. Signal point 301 is the signal point of a knownpilot symbol and signal points 302 are the signal points of 16QAMmodulation symbols. FIG. 4 shows a signal point layout according to the8PSK modulation system on the in-phase I-quadrature Q plane and signalpoint layout of a known pilot symbol. Signal point 401 is the signalpoint of a known pilot symbol and signal points 402 are the signalpoints of 8PSK modulation symbols.

FIG. 5 is a block diagram showing a configuration of the receptionapparatus according to this embodiment. As shown in FIG. 5, thereception apparatus' according to this Embodiment mainly consists ofreception antenna. 501, reception radio section 502, transmission pathdistortion estimation section 503 and detection section 504.

Reception radio section 502 receives the radio signal received byreception antenna 501 as an input, performs predetermined radioprocessing and outputs the in-phase component and the quadraturecomponent of the reception quadrature baseband signal.

Transmission path distortion estimation section 503 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, extracts the signal of the known pilot symbolshown in FIG. 3 and FIG. 4 above, estimates the amount of transmissionpath distortion from the reception condition of the known pilot symboland outputs the amount of transmission path distortion to detectionsection 504.

Detection section 504 receives the in-phase component and the quadraturecomponent of the quadrature baseband signal as inputs, detectsinformation symbols based on the amount of transmission path distortionand outputs a reception digital signal.

Thus, changing the interval of inserting a known pilot symbol and themodulation system of information symbols according to the communicationsituation such as fluctuations in the transmission path and the level ofthe reception signal can improve both the data transmission efficiencyand the quality of data at the same time.

Here, this embodiment explains two kinds of the interval of inserting aknown pilot symbol, but the present invention is not limited to this.Furthermore, this embodiment explains two kinds of the modulation systemof information symbols, 16QAM and the 8PSK modulation, but the presentinvention is not limited to this.

Furthermore, this embodiment only explains the frame configuration ofinformation symbols and a known pilot symbol shown in FIG. 2, but sinceit is also possible to consider a frame configuration in which signalssuch as a symbol for synchronization to adjust timing between thereceiver and transmitter and a symbol to correct an error on thereceiver side are inserted, the present invention is not limited to theframe configuration composed of only information symbols and known pilotsymbol.

Embodiment 2

Embodiment 2 describes a digital radio communication method by which theinterval of inserting a BPSK modulation symbol and the modulation systemof information symbols other than the above BPSK modulation symbol arechanged according to the communication situation.

FIG. 6 is a block diagram showing a configuration of the transmissionapparatus according to this Embodiment. Here, in the transmissionapparatus shown in FIG. 6, the components common to those in thetransmission apparatus shown in FIG. 1 are assigned the same referencenumerals as those in FIG. 1 and their explanations will be omitted.

In the transmission apparatus in FIG. 6, frame configurationdetermination section 601 differs in the way of operation from the frameconfiguration determination section 101 in FIG. 1. Also, when comparedto FIG. 1, the transmission apparatus in FIG. 6 adopts the configurationwith BPSK symbol modulation section 602, instead of pilot symbolgeneration section 103, added.

Frame configuration determination section 601 judges the communicationsituation, determines the interval of inserting a BPSK modulation symboland the modulation system of a transmission digital signal, outputs asignal indicating the determined modulation system to quadraturebaseband modulation section 102 and outputs a signal indicating theinterval of inserting the determined BPSK modulation symbol toquadrature baseband modulation section 102, BPSK symbol modulationsection 602 and frame configuration section 104.

BPSK symbol modulation section 602 performs BPSK-modulation on thetransmission digital signal at the timing indicated from frameconfiguration determination section 601 and outputs the in-phasecomponent and the quadrature component of the BPSK modulation symbol toframe configuration section 104.

FIG. 7 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of this embodiment and showsa time-symbol relationship. (701) is a frame configuration when themodulation system of information symbols is 16QAM and a BPSK modulationsymbol interval is N symbols. (702) is a frame configuration when themodulation system of information symbols is 16QAM and a BPSK modulationsymbol interval is M symbols. (703) is a frame configuration when themodulation system of information symbols is 8PSK modulation and a BPSKmodulation symbol interval is N symbols. (704) is a frame configurationwhen the modulation system of information symbols is 8PSK modulation anda BPSK modulation symbol interval is M symbols. Suppose N<M at thistime.

Frame configuration determination section 601 selects one of (701),(702), (703) or (704) in FIG. 7 as the optimal frame configuration basedon the transmission path information and the request data transmissionspeed information.

For example, in the case of high-speed fading, frame configurationdetermination section 601 sacrifices data transmission efficiency on thereceiving side and selects a frame configuration of either (701) or(703) in FIG. 7 so that the interval of inserting a BPSK modulationsymbol becomes narrower to prevent deterioration of the datademodulation error rate and maintain the quality of data. On the otherhand, in the case of low-speed fading, frame configuration determinationsection 601 selects a frame configuration of either (702) or (704) inFIG. 7 to widen the interval of inserting a BPSK modulation symbol toimprove the data transmission efficiency.

Furthermore, when the level of the reception signal is large, frameconfiguration determination section 601 gives priority to datatransmission efficiency on the receiving side and selects a frameconfiguration of either (701) or (702) in the FIG. 7 adopting 16QAM asthe modulation system of information symbols. On the other hand, whenthe level of the reception signal is small, frame configurationdetermination section 601 gives priority to increasing error resistancewhile sacrificing data transmission efficiency on the receiving side andselects a frame configuration of either (703) or (704) in FIG. 7adopting 8PSK as the modulation system of information symbols.

FIG. 8 shows a signal point layout according to the 16QAM modulationsystem on the in-phase I-quadrature Q plane and signal point layout ofBPSK modulation symbols. Signal points 801 are the signal points of BPSKmodulation symbols and signal points 802 are the signal points of 16QAMmodulation symbols. FIG. 9 shows a signal point layout according to the8PSK modulation system on the in-phase I-quadrature Q plane and signalpoint layout of BPSK modulation symbols. Signal points 901 are thesignal points of BPSK modulation symbols and signal points 902 are thesignal points of 8PSK modulation symbols.

FIG. 10 is a block diagram showing a configuration of the receptionapparatus according to this Embodiment. In the reception apparatus shownin FIG. 10, the components common to the reception apparatus shown inFIG. 5 are assigned the same reference numerals as those in FIG. 5 andtheir explanations will be omitted.

In the reception apparatus in FIG. 10, transmission path distortionestimation section 1001 differs in the way of operation fromtransmission path distortion estimation section 503 in FIG. 5 anddetection section 1002 differs in the way of operation from detectionsection 504 in FIG. 5.

Transmission path distortion estimation section 1001 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, extracts the signals of the BPSK modulationsymbols shown in FIG. 8 and FIG. 9 above, estimates the amount oftransmission path distortion from the reception condition of the BPSKmodulation symbols and outputs the amount of transmission pathdistortion to detection section 1002.

Detection section 1002 receives the in-phase component and thequadrature component of the quadrature baseband signal as inputs,detects information symbols and BPSK modulation symbols based on theamount of transmission path distortion and outputs a reception digitalsignal.

Thus, in this embodiment, by sending information with BPSK modulationsymbols, instead of a known pilot symbol, inserted, it is possible toimprove the transmission speed compared with Embodiment 1.

Here, this embodiment describes two kinds of the interval of insertingBPSK modulation symbols but the present invention is not limited tothis. Also, this embodiment describes two kinds of the modulation systemof information symbols, 16QAM and 8PSK modulation, but the presentinvention is not limited to this.

Furthermore, this embodiment describes the frame configuration of onlyinformation symbols and BPSK modulation symbols shown in FIG. 7 but thepresent invention is not limited to this frame configuration.

Embodiment 3

Embodiment 3 describes a digital radio communication method by which theinterval of inserting QPSK modulation symbols and the modulation systemof information symbols other than the above QPSK modulation symbols arechanged according to the communication situation.

FIG. 11 is a block diagram showing a configuration of the transmissionapparatus according to this Embodiment. In the transmission apparatusshown in FIG. 11, the components common to those in the transmissionapparatus shown in FIG. 1 are assigned the same reference numerals asthose in FIG. 1 and their explanations will be omitted.

In the transmission apparatus in FIG. 11, frame configurationdetermination section 1101 differs in the way of operation from theframe configuration determination section 101 in FIG. 1. Also, whencompared to FIG. 1, the transmission apparatus in FIG. 11 adopts aconfiguration with QPSK symbol modulation section 1102, instead of pilotsymbol generation section 103, added.

Frame configuration determination section 1101 judges the communicationsituation, determines the interval of inserting QPSK modulation symbolsand the modulation system of a transmission digital signal, outputs asignal indicating the determined modulation system to quadraturebaseband modulation section 102 and outputs a signal indicating thedetermined interval of inserting QPSK modulation symbols to quadraturebaseband modulation section 102, QPSK symbol modulation section 1102 andframe configuration section 104.

QPSK symbol modulation section 1102 performs QPSK-modulation on atransmission digital signal at the timing indicated from frameconfiguration determination section 1101 and outputs the in-phasecomponent and the quadrature component of the QPSK modulation symbol toframe configuration section 104.

FIG. 12 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of this embodiment and showsa time-symbol relationship. (1201) is a frame configuration when themodulation system of information symbols is 16QAM and a QPSK modulationsymbol interval is N symbols. (1202) is a frame configuration when themodulation system of information symbols is 16QAM and a QPSK modulationsymbol interval is M symbols. (1203) is a frame configuration when themodulation system of information symbols is 8PSK modulation and a QPSKmodulation symbol interval is N symbols. (1204) is a frame configurationwhen the modulation system of information symbols is 8PSK modulation anda QPSK modulation symbol interval is M symbols. Suppose N<M at thistime.

Frame configuration determination section 1101 selects one of (1201),(1202), (1203) or (1204) in FIG. 12 as the optimal frame configurationbased on the transmission path information and the request datatransmission speed information.

For example, in the case of high-speed fading, frame configurationdetermination section 1101 sacrifices data transmission efficiency onthe receiving side and selects a frame configuration of either (1201) or(1203) in FIG. 12 so that the QPSK modulation symbol insertion intervalbecomes narrower to prevent deterioration of the data demodulation errorrate and maintain the quality of data. On the other hand, in the case oflow-speed fading, frame configuration determination section 1101 selectsa frame configuration of either (1202) or (1204) in FIG. 12 to widen theinterval of inserting QPSK modulation symbols to improve the datatransmission efficiency.

Furthermore, when the level of the reception signal is large, frameconfiguration determination section 1101 gives priority to datatransmission efficiency on the receiving side and selects a frameconfiguration of either (1201) or (1202) in FIG. 12 adopting 16QAM asthe modulation system of information symbols. On the other hand, whenthe level of the reception signal is small, frame configurationdetermination section 1101 gives priority to increasing error resistancewhile sacrificing data transmission efficiency on the receiving side andselects a frame configuration of either (1203) or (1204) in FIG. 12adopting 8PSK as the modulation system of information symbols.

FIG. 13 shows a signal point layout according to the 16QAM modulationsystem on the in-phase I-quadrature Q plane and signal point layout ofQPSK modulation symbols. Signal points 1301 are the signal points ofQPSK modulation symbols and signal points 1302 are the signal points of16QAM modulation symbols. FIG. 14 shows a signal point layout accordingto the 8PSK modulation system on the in-phase I-quadrature Q plane andsignal point layout of QPSK modulation symbols. Signal points 1401 arethe signal points of QPSK modulation symbols and signal points 1402 arethe signal points of 8PSK modulation symbols.

FIG. 15 is a block diagram showing a configuration of the receptionapparatus according to this embodiment. In the reception apparatus shownin FIG. 15, the components common to the reception apparatus shown inFIG. 5 are assigned the same reference numerals as those in FIG. 5 andtheir explanations will be omitted.

In the reception apparatus in FIG. 15, transmission path distortionestimation section 1501 differs in the way of operation fromtransmission path distortion estimation section 503 in FIG. 5 anddetection section 1502 differs in the way of operation from detectionsection 504 in FIG. 5.

Transmission path distortion estimation section 1501 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, extracts the signals of the QPSK modulationsymbols shown in FIG. 13 and FIG. 14 above, estimates the amount oftransmission path distortion from the reception condition of the QPSKmodulation symbols and outputs the amount of transmission pathdistortion to detection section 1502.

Detection section 1502 receives the in-phase component and thequadrature component of the quadrature baseband signal as inputs,detects information symbols and QPSK modulation symbols based on theamount of transmission path distortion and outputs a reception digitalsignal.

Thus, in this embodiment, by sending information with QPSK modulationsymbols, instead of a known pilot symbol, inserted, it is possible toimprove the transmission speed compared with Embodiment 1 and Embodiment2.

Here, this embodiment describes two kinds of the interval of insertingQPSK modulation symbols but the present invention is not limited tothis. Also, this embodiment describes two kinds of the modulation systemof information symbols, 16QAM and 8PSK modulation, but the presentinvention is not limited to this.

Furthermore, this embodiment describes the frame configuration of onlyinformation symbols and QPSE modulation symbols shown in FIG. 12 but thepresent invention is not limited to this frame configuration.

Embodiment 4

Embodiment 4 describes a digital radio communication method by which themodulation system of information symbols is changed according to thecommunication situation and when the modulation system of informationsymbols uses 8 or more values, a known pilot symbol is inserted with theinsertion interval changed according to the communication situation.

FIG. 16 is a block diagram showing a configuration of the transmissionapparatus according to this Embodiment. In the transmission apparatusshown in FIG. 16, the components common to those in the transmissionapparatus shown in FIG. 1 are assigned the same reference numerals asthose in FIG. 1 and their explanations will be omitted.

In the transmission apparatus in FIG. 16, frame configurationdetermination section 1601 differs in the way of operation from theframe configuration determination section 101 in FIG. 1.

Frame configuration determination section 1601 determines the modulationsystem of a transmission digital signal based on the communicationsituation and outputs a signal indicating the determined modulationsystem to quadrature baseband modulation section 102. Also, when thedetermined modulation system uses 8 or more values, frame configurationdetermination section 1601 determines the interval of inserting a pilotsymbol based on the communication situation and outputs a signalindicating the determined interval of inserting the pilot symbol toframe configuration section 104. Also, when the determined modulationsystem uses 8 fewer values, frame configuration determination section1601 outputs a signal giving an instruction for stopping the generationof pilot symbols to pilot symbol generation section 103.

Pilot symbol generation section 103 generates a pilot symbol knownbetween the transmitting and receiving sides and outputs the in-phasecomponent and the quadrature component of the known pilot symbol toframe configuration section 104. However, when instructed to stop thegeneration of pilot symbols from frame configuration determinationsection 1601, pilot symbol generation section 103 stops operation.

FIG. 17 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of this embodiment and showsa time-symbol relationship. (1701) is a frame configuration when themodulation system of information symbols is BPSK. (1702) is a frameconfiguration when the modulation system of information symbols is QPSK.

The ranking of the frame configurations shown in FIG. 2 and FIG. 17 indescending order of resistance to fading speed is (1701), (1702), (203),(201), (204) and (202). Furthermore, the ranking in descending order oferror resistance is (1701), (1702), (203), (204), (201) and (202). Onthe other hand, the ranking in descending order of data transmissionefficiency on the receiving side is (202), (201), (204), (203), (1702)and (1701).

Frame configuration determination section 1601 selects one of (201),(202), (203) or (204) in FIG. 2 of (1701) or (1702) in FIG. 17 above asthe optimal frame configuration based on the transmission pathinformation and the request data transmission speed information.

FIG. 18 shows a signal point layout according to the BPSK modulationmethod on the in-phase I-quadrature Q plane and signal points 1801 arethe signal points of BPSK symbols.

FIG. 19 shows a signal point layout according to the QPSK modulationmethod on the in-phase I-quadrature Q plane and signal points 1901 arethe signal points of QPSX symbols.

FIG. 20 is a block diagram showing a configuration of the receptionapparatus according to this embodiment. In the reception apparatus shownin FIG. 20, the components common to those in the reception apparatusshown in FIG. 5 are assigned the same reference numerals as those inFIG. 5 and their explanations will be omitted.

In the reception apparatus in FIG. 20, transmission path distortionestimation section 2001 differs in the way of operation fromtransmission path estimation section 503 in FIG. 5 and detection section2002 differs in the way of operation from detection section 504 in FIG.5.

Transmission path distortion estimation section 2001 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, estimates the amount of transmission pathdistortion from the reception condition of the BPSK modulation symbolshown in FIG. 18 or the QPSK modulation symbol shown in FIG. 19 andoutputs the amount of transmission path distortion to detection section2002.

Detection section 2002 receives the in-phase component and thequadrature component of the quadrature baseband signal as inputs,detects information symbols based on the amount of transmission pathdistortion and outputs a reception digital signal.

In this way, by changing the modulation system of information symbolsaccording to the communication situation such as fluctuations in thetransmission path and the level of the reception signal, inserting aknown pilot symbol when the information symbol modulation system is amulti-value modulation system with 8 or more values and changing theinterval of inserting the above known pilot symbol according to thecommunication situation, it is possible to improve both the datatransmission efficiency and the quality of data at the same time.

Here, in this embodiment, the transmission apparatus in FIG. 16 can alsohave a configuration equipped with BPSK symbol modulation section 602shown in FIG. 6 instead of pilot symbol generation section 103.

In this case, frame configuration determination section 1601 determinesthe modulation system of the transmission digital signal based on thecommunication situation. For example, frame configuration determinationsection 1601 selects one of (701), (702), (703) or (704) in FIG. 7 aboveor (1701) or (1702) in FIG. 17 as the optimal frame configuration.

Then, frame configuration determination section 1601 outputs the signalsindicating the determined modulation system to quadrature basebandmodulation section 102. Also, when the determined modulation system uses8 or more values, frame configuration determination section 1601determines the interval of inserting BPSK modulation symbols based onthe communication situation and outputs a signal indicating thedetermined interval of inserting the BPSK nodulation symbols to BPSKsymbol modulation section 602 and frame configuration section 104.Furthermore, when the determined modulation system is 8 fewer values,frame configuration determination section 1601 outputs a signal givingan instruction for stopping the generation of BPSK modulation symbols toBPSK symbol modulation section 602.

BPSK symbol modulation section 602 performs BPSK-modulation on atransmission digital signal at the timing indicated from frameconfiguration determination section 1601 and outputs the in-phasecomponent and the quadrature component of the BPSK modulation symbols toframe configuration section 104. However, when instructed to stop thegeneration of BPSK modulation symbols from frame configurationdetermination section 1601, BPSK symbol modulation section 602 stopsoperation.

Transmission path distortion estimation section 2001 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, estimates the amount of transmission pathdistortion from the reception condition of the BPSK modulation symbolsshown in FIG. 8 and FIG. 9 above, the BPSK modulation symbols shown inFIG. 18 or the QPSK modulation symbols shown in FIG. 19 and outputs theamount of transmission path distortion to detection section 2002.

Furthermore, in this embodiment, the transmission apparatus in FIG. 16.can also have a configuration equipped with QPSK symbol modulationsection 1102 shown in FIG. 11 instead of pilot symbol generation section103.

In this case, frame configuration determination section 1601 determinesthe modulation system of the transmission digital signal based on thecommunication situation. For example, frame configuration determinationsection 1601 selects one of (1201), (1202), (1203) or (1204) in FIG. 12above or (1701) or (1702) in FIG. 17 as the optimal frame configuration.

Then, frame configuration determination section 1601 outputs a signalindicating the determined modulation system to quadrature basebandmodulation section 102. Also, when the determined modulation system uses8 or more values, frame configuration determination section 1601determines the interval of inserting QPSK modulation symbols based onthe communication situation and outputs a signal indicating thedetermined interval of inserting the QPSK symbols to QPSK symbolmodulation section 1102 and frame configuration section 104. Also, whenthe determined modulation system is 8 fewer values, frame configurationdetermination section 1601 outputs a signal giving an instruction forstopping the generation of QPSK modulation symbols to QPSK symbolmodulation section 1102.

QPSK symbol modulation section 1102 performs QPSK-modulation on atransmission digital signal at the timing indicated from frameconfiguration determination section 1601 and outputs the in-phasecomponent and the quadrature component of the QPSK modulation symbols toframe configuration section 104. However, when instructed to stopgenerating QPSK modulation symbols from frame configurationdetermination section 1601, QPSK symbol modulation section 1102 stopsoperation.

Transmission path distortion estimation section 2001 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, estimates the amount of transmission pathdistortion from the reception condition of the QPSK modulation symbolsshown in FIG. 13 or FIG. 14 and the BPSK modulation symbols shown inFIG. 18 or the QPSK modulation symbol shown in FIG. 19 and outputs theamount of transmission path distortion to detection section 2002.

Here, this embodiment explains two kinds of the interval of inserting aknown pilot symbol, but the present invention is not limited to this.Also, this embodiment explains two kinds of the multi-value modulationsystem with 8 or more values of information symbols, 16QAM and the 8PSKmodulation, but the present invention is not limited to this.

Furthermore, this embodiment describes the frame configurations in FIG.2, FIG. 7, FIG. 12 and FIG. 17 but the present invention is not limitedto these frame configurations.

Furthermore, the BPSK modulation method and the QPSK modulation methodof the modulation system of information symbols of the present inventionare not limited to the signal point layouts shown in FIG. 18 and FIG. 19but π/2 shift BPSK modulation or π/4 shift QPSK modulation can also beused.

Embodiment 5

Embodiment 5 describes a digital radio communication method by which theinterval of inserting a known pilot symbol, the number of signal pointswith one symbol immediately before and after a known pilot symbol(hereinafter referred to as “symbols before and after a pilot”) andsignal point layout and the modulation system of information symbolsother than those symbols are changed.

FIG. 21 is a block diagram showing a configuration of the transmissionapparatus according to this embodiment. In the transmission apparatusshown in FIG. 21, the components common to those in the transmissionapparatus shown in FIG. 1 are assigned the same reference numerals asthose shown in FIG. 1 and their explanations will be omitted.

In the transmission apparatus in FIG. 21, frame configurationdetermination section 2101 differs in the way of operation from frameconfiguration determination section 101 in FIG. 1. Furthermore, thetransmission apparatus in FIG. 21 adopts a configuration with symbolsbefore and after a pilot modulation section 2102 added compared to FIG.1.

Frame configuration determination section 2101 determines the intervalof inserting a known pilot symbol and the modulation system of atransmission digital signal based on the communication situation. Inthis case, frame configuration determination section 2101 uses differentmodulation systems for symbols before and after a pilot and for otherinformation symbols.

Then, frame configuration determination section 2101 outputs a signalindicating the modulation system of symbols before and after a pilot tosymbols before and after a pilot modulation section 2102, outputs asignal indicating the modulation system of other information symbols toquadrature baseband modulation section 102 and outputs a signalindicating the interval of inserting the determined known pilot symbolto symbols before and after a pilot modulation section 2102 and frameconfiguration section 104.

Symbols before and after a pilot modulation section 2102 modulates on atransmission digital signal by predetermined modulation system at thetiming indicated from frame configuration determination section 2101 andoutputs the in-phase component and the quadrature component of thesymbols before and after a pilot to frame configuration section 104.

FIG. 22 illustrates examples of a frame configuration of a signaltransmitted from the transmission apparatus of this embodiment and showsa time-symbol relationship. (2201) is a frame configuration when themodulation system of information symbols is 16QAM and a known pilotsymbol interval is N symbols. (2202) is a frame configuration when themodulation system of information symbols is 16QAM and a known pilotsymbol interval is 1 symbols. (2203) is a frame configuration when themodulation system of information symbols is 8PSK modulation and a knownpilot symbol interval is N symbols. (2204) is a frame configuration whenthe modulation system of information symbols is 8PSK modulation and aknown pilot symbol interval is M symbols. Suppose N<M at this time.

Signal point 2211 is 1 symbol immediately before the known pilot symbolwhen the information symbol modulation system is 16QAM and signal point2212 is 1 symbol immediately after the known pilot symbol when theinformation symbol modulation system is 16QAM. Signal point 2213 is 1symbol immediately before the known pilot symbol when the informationsymbol modulation system is 8PSK modulation and signal point 2214 is 1symbol immediately after the known pilot symbol when the informationsymbol modulation system is 8PSK modulation.

Frame configuration determination section 2101 selects one of (2201),(2202), (2203) or (2204) in FIG. 22 as the optimal frame configurationbased on the transmission path information and the request datatransmission speed information.

For example, in the case of high-speed fading, frame configurationdetermination section 2101 sacrifices data transmission efficiency onthe receiving side and selects a frame configuration of either (2201) or(2203) in FIG. 22 so that the interval of inserting a known pilot symbolbecomes narrower to prevent deterioration of the data demodulation errorrate and maintain the quality of data. On the other hand, in the case oflow-speed fading, frame configuration determination section 2101 selectsa frame configuration of either (2202) or (2204) in FIG. 22 to widen theinterval of inserting a known pilot symbol to improve the datatransmission efficiency.

Furthermore, when the level of the reception signal is large, frameconfiguration determination section 2101 gives priority to datatransmission efficiency on the receiving side and selects a frameconfiguration of either (2201) or (2202) in FIG. 22 adopting 16QAM asthe modulation system of information symbols. On the other hand, whenthe level of the reception signal is small, frame configurationdetermination section 2101 gives priority to increasing error resistancewhile sacrificing data transmission efficiency on the receiving side andselects a frame configuration of either (2203) or (22041 in FIG. 22adopting 8PSK as the modulation system of information symbols.

FIG. 23 shows a signal point layout according to the 16QAM modulationmethod on the in-phase I-quadrature Q plane and a signal point layoutaccording to a known pilot symbol and a signal point layout of symbolsbefore and after a pilot. Signal point 2301 is the signal point of aknown pilot symbol, signal points 2302 are the signal points of 16QAMmodulation symbols and signal points 2303 are the signal points ofsymbols before and after a pilot.

FIG. 24 shows a signal point layout according to the 8PSK modulationsystem on the in-phase I-quadrature Q plane, a signal point layout of aknown pilot symbol and a signal point layout of symbols before and aftera pilot. Signal points 2401, 2401-A and 2401-B are the signal points of8PSK modulation symbols, 2401-A is the signal point of the known pilotsymbol, 2401-A and 2401-B are the signal points of symbols before andafter a pilot and straight line 2402 is the straight line formed bylinking the signal point of the known pilot symbol and the origin on thein-phase I-quadrature Q plane.

FIG. 25 is a block diagram showing a configuration of the receptionapparatus according to this embodiment, In the reception apparatus shownin FIG. 25, the components common to those in the reception apparatusshown in FIG. 5 are assigned the same reference numerals as those shownin FIG. 5 and their explanations will be omitted.

In the reception apparatus in FIG. 25, transmission path estimationsection 2501 differs in the way of operation from transmission pathestimation section 503 and detection section 2502 differs in the way ofoperation from detection section 504 in FIG. 5.

Transmission path distortion estimation section 2501 receives thein-phase component and the quadrature component of the quadraturebaseband signal as inputs, extracts the signal of the known pilot symbolshown in FIG. 23 and FIG. 24 above, estimates the amount of transmissionpath distortion from the reception condition of the known pilot symboland outputs the amount of transmission path distortion to detectionsection 2502.

Detection section 2502 receives the in-phase component and thequadrature component of the quadrature baseband signal as inputs,detects information symbols including symbols before and after a pilotbased on the amount of transmission path distortion and outputs areception digital signal.

Thus, changing the interval of inserting a known pilot symbol and themodulation system of information symbols according to the communicationsituation such as fluctuations in the transmission path and the level ofthe reception signal can improve both the data transmission efficiencyand the quality of data at the same time.

Furthermore, as shown in FIG. 23 and FIG. 24, by arranging two or moresignal points before and after a pilot on the straight line formed bylinking the origin and the signal point of the known pilot symbol on thein-phase I-quadrature Q plane, it is possible for the receptionapparatus in FIG. 25 to suppress deterioration of the estimationaccuracy of reference phase and the amount of frequency offset by thepilot symbol, even if symbol synchronization is not establishedcompletely when a reference phase and the amount of frequency offset isestimated from the pilot signal. When detection section 116 performsdetection, this allows the bit error rate characteristic based on thecarrier-to-noise ratio to be improved.

Here, this embodiment can be combined with Embodiment 4 above. That is,when the determined modulation system uses 8 or more values, frameconfiguration determination section 2101 in FIG. 21 determines theinterval of inserting a pilot symbol based on the communicationsituation and outputs a signal indicating the interval of inserting thedetermined pilot symbol to symbols before and after a pilot modulationsection 2102 and frame configuration section 104. Furthermore, when thedetermined modulation system uses 8 fewer values, frame configurationdetermination section 2101 outputs a signal giving an instruction forstopping the generation of pilot symbols to symbols before and after apilot modulation section 2102 and pilot symbol generation section 103.

Pilot symbol generation section 103 generates a pilot symbol knownbetween the transmitting and receiving sides and outputs the in-phasecomponent and the quadrature component of the known pilot symbol toframe configuration section 104. However, when instructed to stop thegeneration of pilot symbols from frame configuration determinationsection 2101, pilot symbol generation section 103 stops operation.

Symbols before and after a pilot modulation section 2102 performsBPSK-modulation or QPSK-modulation on a transmission digital signal atthe timing indicated from frame configuration determination section 2101and outputs the in-phase component and the quadrature component of thesymbols before and after a pilot to frame configuration section 104.However, when instructed to stop the generation of pilot symbols fromframe configuration determination section 2101, symbols before and aftera pilot modulation section 2102 stops operation.

This allows the effect of Embodiment 4 to be attained in addition to theeffect of this embodiment as described above.

Here, this embodiment describes two kinds of modulation system ofinformation symbols, 16QAM and 8PSK modulation, but the presentinvention is not limited to this.

Furthermore, this embodiment explains only the configuration ofinformation symbols, a known pilot symbol, symbols before and after apilot in FIG. 22, but the frame configuration of the present inventionis not limited to the frame configuration composed of only informationsymbols, a known pilot symbol, symbols before and after a pilot.

As described above, according to the present invention, by changing theinterval of inserting a known pilot symbol, BPSK modulation symbols orQPSK modulation symbols and the modulation system of information symbolsaccording to the communication situation of fluctuations in thetransmission path and the level of the reception signal, etc., it ispossible to improve both the data transmission efficiency and thequality of data at the same time.

The present invention is not limited to the above described embodiments,and various variations and modifications may be possible withoutdeparting from the scope of the present invention.

This application is based on the Japanese Patent. Application No. HEI11-213289 filed on Jul. 28, 1999, entire content of which is expresslyincorporated by reference herein.

What is claimed is:
 1. A transmission method comprising: modulating atransmission signal using a modulation scheme selected from a pluralityof modulation schemes, to generate a first symbol sequence; providing atleast one second symbol generated using a phase shift keying (PSK)modulation scheme; inserting the second symbol in the first symbolsequence to generate a modulation signal, and transmitting themodulation signal.
 2. The transmission method according to claim 1,wherein the first symbol sequence is arranged on a time axis.
 3. Thetransmission method according to claim 1, wherein the PSK modulationscheme is a binary phase shift keying (BPSK) modulation or a quadraturephase shift keying (QPSK) modulation.
 4. The transmission methodaccording to claim 1, wherein the first symbol comprising a quadraturebaseband signal.
 5. The transmission method according to claim 1,further comprising: changing an insertion interval of the second symbolin the first symbol sequence to generate the modulation signal.
 6. Thetransmission method according to claim 1, wherein the modulation schemefor the transmission signal is selected based on condition oftransmission path of the modulation signal.
 7. The transmission methodaccording to claim 1, wherein the second symbol is for one of more of:estimating distortion of transmission path of the modulation signal at areception apparatus, calculating a phase and an amount of frequencyoffset in the modulation signal at the reception apparatus,synchronizing timing between the reception apparatus and a transmissionapparatus, and correcting errors in the modulation signal at thereception apparatus.
 8. A transmission apparatus configured to: modulatea transmission signal using a modulation scheme selected from aplurality of modulation schemes, to generate a first symbol sequence;insert a second symbol, generated using a phase shift keying (PSK)modulation scheme, in the first symbol sequence to generate a modulationsignal; and transmit the modulation signal.
 9. The transmissionapparatus according to claim 8, wherein the first symbol sequence isarranged on a time axis.
 10. The transmission apparatus according toclaim 8, wherein the PSK modulation scheme is a binary phase shiftkeying (BPSK) modulation or a quadrature phase shift keying (QPSK)modulation.
 11. The transmission apparatus according to claim 8, whereinthe first symbol comprising a quadrature baseband signal.
 12. Thetransmission apparatus according to claim 8, further configured tochange an insertion interval of the second symbol in the first symbolsequence to generate the modulation signal.
 13. The transmissionapparatus according to claim 8, wherein the modulation scheme for thetransmission signal is selected based on condition of transmission pathof the modulation signal.
 14. The transmission apparatus according toclaim 8, wherein the second symbol is for one of more of: estimatingdistortion of transmission path of the modulation signal at a receptionapparatus, calculating a phase and an amount of frequency offset in themodulation signal at the reception apparatus, synchronizing timingbetween the reception apparatus and the transmission apparatus, andcorrecting errors in the modulation signal at the reception apparatus.15. The transmission apparatus according to claim 8, comprising: amodulator to modulate the transmission signal, and a processor to insertthe second symbol in the first symbol sequence.
 16. A reception methodcomprising: receiving at a reception apparatus a modulation signaltransmitted from a transmission apparatus; extracting a second symbolfrom the received modulation signal and estimating condition oftransmission path of the modulation signal using the second symbol; andoutputting a received data signal from a first symbol sequence includedin the modulation signal, using transmission path estimation, whereinthe modulation signal includes: at least one second symbol generatedusing a phase shift key (PSK) modulation scheme, inserted in the firstsymbol sequence generated using a modulation scheme selected from aplurality of modulation schemes.
 17. The reception method according toclaim 16, wherein the plurality of modulation schemes include M-arymodulation schemes of two or more kinds.
 18. The reception methodaccording to claim 16, wherein the PSK modulation scheme is a binaryphase shift keying (BPSK) modulation or a quadrature phase shift keying(QPSK) modulation.
 19. The reception method according to claim 16,wherein the first symbol sequence is arranged on a time axis.
 20. Thereception method according to claim 16, wherein the data signal is aquadrature baseband signal.
 21. The reception method according to claim16, wherein the modulation scheme for generating the first symbolsequence is selected based on condition of the transmission path of themodulation signal.
 22. The reception method according to claim 16,wherein the modulation signal is generated by changing an insertioninterval of the second symbol in the first symbol sequence.
 23. Thereception method according to claim 16, wherein the second symbol is forone of more of: estimating distortion of transmission path of themodulation signal at the reception apparatus, calculating a phase and anamount of frequency offset in the modulation signal at the receptionapparatus, synchronizing timing between the reception apparatus and thetransmission apparatus, and correcting errors in the modulation signalat the reception apparatus.
 24. A reception apparatus comprising: areceiver to receive a modulation signal transmitted from a transmissionapparatus; a transmission path estimator that extracts a second symbolfrom the received modulation signal and estimates transmission path ofthe modulation signal using the second symbol; and a detector thatoutputs a received data signal from a first symbol sequence included inthe modulation signal, using transmission path estimation, wherein themodulation signal includes: at least one second symbol, generated usinga phase shift keying (PSK) modulation scheme, inserted in a first symbolsequence generated using a modulation scheme selected from a pluralityof modulation scheme.
 25. The reception apparatus according to claim 24,wherein the plurality of modulation schemes include M-ary modulationschemes of two or more kinds.
 26. The reception apparatus according toclaim 24, wherein the PSK modulation scheme is a binary phase shiftkeying (BPSK) modulation or a quadrature phase shift keying (QPSK)modulation.
 27. The reception apparatus according to claim 24, whereinthe first symbol sequence is arranged on a time axis.
 28. The receptionapparatus according to claim 24, wherein the data signal is a quadraturebaseband signal.
 29. The reception apparatus according to claim 24,wherein the modulation scheme for generating the first symbol sequenceis selected based on condition of the transmission path of themodulation signal.
 30. The reception apparatus according to claim 24,wherein the modulation signal is further generated by changing aninsertion interval of the second symbol in the first symbol sequence.31. The reception apparatus according to claim 24, wherein the secondsymbol s for one of more of: estimating distortion of transmission pathof the modulation signal at the reception apparatus, calculating a phaseand an amount of frequency offset in the modulation signal at thereception apparatus, synchronizing timing between the receptionapparatus and the transmission apparatus and correcting errors in themodulation signal at the reception apparatus.